A current trend in the electronics industry is to reduce the power requirements of integrated circuitry. In order to reduce power consumption, integrated circuits are being designed to use lower voltage supply levels such as 3.3 volts instead of 5 volts, for example.
Many operations, however, require voltages greater than that provided by the lower voltage power supplies. For example, flash electrically-erasable programmable read only memory (flash EEPROM) requires approximately 12 volts for erase and programming operations.
Charge pump technology permits the generation of voltages having a magnitude greater than that of the power supply. Through the use of charge pump circuitry 12 volts can be generated from 3.3 volts by using one or more charge pump stages.
In the electronics field, the practitioner often needs to generate a number of voltages from one available power supply voltage. For example, computer memory circuitry might require one voltage for reading, another voltage for writing, and yet a third voltage for erasing the memory. Alternatively, different components of the computer system (such as different types of memory) may have power supply requirements that differ from each other and from the available power supply voltage.
Another factor to consider when designing integrated circuits is that even though a trend might indicate a general acceptance of a progression towards another power supply level, there may be an established base of circuitry that will not readily change. For example, although a current trend may be moving towards a 3.3 volt power supply system, there may be an established base of hardware dependent upon a 5 volt power supply.
One prior art method used to generate multiple higher voltage levels from a single power supply voltage is to use a number of charge pump circuits each having a fixed number of stages. One disadvantage of this method is that each charge pump circuit requires a dedicated space in the integrated circuit. Another disadvantage is that the integrated circuit might not be able to be interchangeably used with both a 3.3 volt power supply and a 5 volt power supply without additional external circuitry. For example, a manufacturer might find it advantageous to provide a single flash memory product that could accommodate different power supplies.
Another prior art method used to generate multiple higher voltage levels from a single power supply voltage is to use one charge pump circuit that used a fixed number of stages to generate a voltage level. Other voltage levels are provided by using voltage divider networks in conjunction with the single charge pump. One disadvantage of this method is that power is wasted on the voltage divider networks. Another disadvantage is that the fixed stage method typically sacrifices performance at one power supply voltage to accommodate another power supply voltage.